231 Climbing Manifold Pressure

[Bob]

I have an issue with my manifold pressure "running away".  

In steady flight the manifold pressure and fuel flow raise on their own. The throttle is locked, no slop in control linkage, fixed wastegate is adjusted properly, the Sid97 fuel setup is setup &proper, no induction or exhaust leaks.   

Happens more frequently at 25-50 LOP.  Happens more at higher power settings.

When the temps raise I have 3 options to lower rapidly and bring MP and fuel flow back to where I set them:

1) Reduce power

2) Open cowl flaps to 1/2 position

3) Turn on low boost pump

Anyone ever experience this on their 231? 

Please watch this video for an example of what I experience:      IMG_0310.MOV

or

https://1drv.ms/v/s!AoWXUWpPMbo_wWj244CrCs_DNRKd

[231LV]

Yes...I notice a "creep" as MP increases. I attributed it to a friction cable slipping. It's annoying but an occasional reset solves my problem

[jlunseth]

I see a little bit of creep also.  One thing to remember is that MP and fuel flow are interlinked in the 231, so if MP increases, fuel flow is going to increase.  All this means is that the culprit is probably in the system that controls MP, and there is no problem with your fuel flow.

Like 231LV I have seen this from time to time, and a reset once or twice normally does it.  If it keeps creeping, then you should probably have your Merlyn checked.  

It can be the other way around, the fuel flow can creep.  I had an inexplicable problem for awhile where my fuel flow varied quite a bit, and the MP did try to follow the fuel flow around, but the response of the MP to changes in the fuel flow was not very rapid or dramatic.

 

[Cardinal767]

I’ve had the same issue, but not to the same extreme. I don’t operate the same settings as in the video. I’m new to the 231 and have a new -LB engine installed. I have a 830 to monitor everything, but I must have it setup wrong. My 65% is around 27”-29” @ 8.5 to 9.5 gph 50 LOP.

I’ve been wondering the cause myself. The biggest change I see is in rough air with speed changes caused by the AP trying to hold altitude. Ram air into the cowling has its affects.

 I do know that in LOP, an increase in fuel flow adds heat energy to the turbo. That increases the MP, and then of course fuel flow increases. I have to play with it, but thankfully I’m not dealing with CHT’s you’re dealing with. When temps get too high, I continue to lean beyond 50 LOP to see if the CHT’s drop or it gets rough.

 

Edited April 4, 2018 by Cardinal767

[Bob]

231LV- On mine, the friction lock is strong and no slop in the cable.

jlunseth- That's the problem, is the FF changing and pulling the MP with it or The MP changing.  A little creep is normal and expect some MP fluctuation, but my MP moves 3-4 inches in one minute.  I typically have to pull power and re-setup controls about every 4-6 minutes. AKA 10-12 time per hour.

Cardinal767- I understand that if I go leaner or reduce power or go ROP, the CHT's will come down.  A typical flight I am in the area of CHT's at 365, TIT at 1580.  Your 830 percentage of HP can only be setup to be accurate for either ROP or LOP.  It can not be set to read accurate for both!  Mine is set up for LOP percentage of power.

[kortopates]

@Bob you need to download your data and verify, but it looks like FF is driving MAP up just as @jlunseth suggest. They are entirely related and @Cardinal767 explanation of why increasing FF will push TIT which will push up MAP is spot on. The more HP or higher MAP and more LOP the engine is the more sensitive it is simply because temps drop off more rapidly with increasing LOP,  while in contrast operating ROP temperatures are more flat with small mixture changes. 

very correct on the need to set up EDM HP constant before trying to use it.  

[jlunseth]

1 hour ago, Bob said:

 

jlunseth- That's the problem, is the FF changing and pulling the MP with it or The MP changing.  A little creep is normal and expect some MP fluctuation, but my MP moves 3-4 inches in one minute.  I typically have to pull power and re-setup controls about every 4-6 minutes. AKA 10-12 time per hour.

Cardinal767- I understand that if I go leaner or reduce power or go ROP, the CHT's will come down.  A typical flight I am in the area of CHT's at 365, TIT at 1580.  Your 830 percentage of HP can only be setup to be accurate for either ROP or LOP.  It can not be set to read accurate for both!  Mine is set up for LOP percentage of power.

Well, I looked at your first post and saw that you said you have a fixed wastegate.  If that is so, then you don’t have a Merlyn and my comments about that are incorrect.  The problem may very well be in your fuel flow.  I noticed at the end of the video when MP and fuel flow start spinning up, the fuel flow is increasing swiftly.  Have you tried adjusting the red knob (fuel flow) rather than adjusting the throttle?  Because that appears to be where the runaway starts.  

[Bob]

2 hours ago, jlunseth said:

Well, I looked at your first post and saw that you said you have a fixed wastegate.  If that is so, then you don’t have a Merlyn and my comments about that are incorrect.  The problem may very well be in your fuel flow.  I noticed at the end of the video when MP and fuel flow start spinning up, the fuel flow is increasing swiftly.  Have you tried adjusting the red knob (fuel flow) rather than adjusting the throttle?  Because that appears to be where the runaway starts.  

Ah, the red knob, no I did not try it, but a great idea!  This is why I have posted this topic, to get some ideas to further troubleshoot or a direction for possible cause.  On my next test flight I will try to reduce fuel and see what happens.  The low boost pump may be doing that since it is set a tad lower, in the area of 10 gph.  The thing that has me puzzled is, if it is fuel, why does the fuel and MP immediately drop when I open the cowl flaps. 

I do have a Merlyn wastegate, but it was removed and the factory fixed unit was installed and adjusted to eliminate variables.

[Cardinal767]

5 hours ago, kortopates said:

@Bob you need to download your data and verify, but it looks like FF is driving MAP up just as @jlunseth suggest. They are entirely related and @Cardinal767 explanation of why increasing FF will push TIT which will push up MAP is spot on. The more HP or higher MAP and more LOP the engine is the more sensitive it is simply because temps drop off more rapidly with increasing LOP,  while in contrast operating ROP temperatures are more flat with small mixture changes. 

very correct on the need to set up EDM HP constant before trying to use it.  

I setup the EDM HP to the ROP constant for break in and have not changed it. The FF, MAP, and airspeed are pretty close to what is listed in the POF. I've kept the settings because ROP is the dangerous side of an engines life. Also I've noticed I can't run smooth LOP below 2500 rpm if I go above the upper teen flight levels, so I'll fly ROP then.

In cruise, I pull back to 70% (125* ROP/12.7gph)  then do the big pull to 8.0gph(60+ LOP) below FL180. I'll check peak from the LOP side, then set in 30*-50* LOP(usually around 8.5 gph) knowing I'll drop below 70% HP. Airspeed drop matches the POH for about 60's% HP (155kts-165kts). CHT's are quite nice, OAT:-10, CHT's low 300's(#5 and#6: upper 200's), OAT: +10, CHT's mid 300's. Oil temps 150f-170f, at OAT:-20 I've seen 138f.

Is 29.0" MAP, 8.5gph FF a correct power setting for around 65% LOP?

I do have to deal with the MP creeping up, then dropping, with only 200 hours on the engine I wouldn't image the turbo is coked up since I do the 5 minute cool down per the POH. 

[kortopates]

4 minutes ago, Cardinal767 said:

I setup the EDM HP to the ROP constant for break in and have not changed it. The FF, MAP, and airspeed are pretty close to what is listed in the POF. I've kept the settings because ROP is the dangerous side of an engines life. Also I've noticed I can't run smooth LOP below 2500 rpm if I go above the upper teen flight levels, so I'll fly ROP then.

In cruise, I pull back to 70% (125* ROP/12.7gph)  then do the big pull to 8.0gph(60+ LOP) below FL180. I'll check peak from the LOP side, then set in 30*-50* LOP(usually around 8.5 gph) knowing I'll drop below 70% HP. Airspeed drop matches the POH for about 60's% HP (155kts-165kts). CHT's are quite nice, OAT:-10, CHT's low 300's(#5 and#6: upper 200's), OAT: +10, CHT's mid 300's. Oil temps 150f-170f, at OAT:-20 I've seen 138f.

Is 29.0" MAP, 8.5gph FF a correct power setting for around 65% LOP?

I do have to deal with the MP creeping up, then dropping, with only 200 hours on the engine I wouldn't image the turbo is coked up since I do the 5 minute cool down per the POH. 

Sounds like you are setting up to verify how much LOP correctly from the lean side.

But 8.5 GPH is only 55% power. At 55% or even uptp 60% power (9.2 GPH) you'll do better to fly at peak or more specifically, from the LOP side, enrichen just till the richest cyl peaks getting the rest on the LOP side rather than ROP side. To calculate LOP % power with your 7.5 compression ratio = 13.7 * FFgph / 210hp

For higher power settings, both LOP and ROP,  I suggest using Gami's recommended and FAA approved number which you can get here http://www.gami.com/gamijectors/afms - gamijectors rev ir.pdf 

[Cardinal767]

13 minutes ago, kortopates said:

Sounds like you are setting up to verify how much LOP correctly from the lean side.

But 8.5 GPH is only 55% power. At 55% or even uptp 60% power (9.2 GPH) you'll do better to fly at peak or more specifically, from the LOP side, enrichen just till the richest cyl peaks getting the rest on the LOP side rather than ROP side. To calculate LOP % power with your 7.5 compression ratio = 13.7 * FFgph / 210hp

For higher power settings, both LOP and ROP,  I suggest using Gami's recommended and FAA approved number which you can get here http://www.gami.com/gamijectors/afms - gamijectors rev ir.pdf 

Thank you sir, I'll put the 13.7 x FF/ 210 on my performance chart in the POH. Some how the Gami POH Supplement did not make it into my POH, I'll fix that tomorrow. As you can tell, I'm conservative power operator and new to LOP operations, I want my -LB to last a long time.

[Bob]

5 minutes ago, Cardinal767 said:

Thank you sir, I'll put the 13.7 x FF/ 210 on my performance chart in the POH. Some how the Gami POH Supplement did not make it into my POH, I'll fix that tomorrow. As you can tell, I'm conservative power operator and new to LOP operations, I want my -LB to last a long time.

The numbers for fuel flow and percentage of HP are on a label, just to the right of my engine monitor, on my video.  In my opinion, 10 GPH is a good number to remember and use and produces 65% power.

[kortopates]

3 hours ago, Bob said:

The thing that has me puzzled is, if it is fuel, why does the fuel and MP immediately drop when I open the cowl flaps.

I've seen this before caused by a leakage in the Merlyn pneumatic line or a UDP leakage. Make sure you don't have any leakage in the Merlyn lines and that the both pressurized mag hoses are connected.

[ziggysanchez]

I had (have) this exact same problem. I did have my wastegate sent to merlyn for IRAN. They found a pin hole leak and replaced some parts. While the repair improved my situation somewhat it didn't completely fix it. If I set the MP high (33" ) and set FF to keep TIT below 1600 and CHT's at or below 350 (usually 10.5 to 11gph) with cowl flaps closed it will still try to runaway on me. I've just chalked it up to the wastegate not liking higher MP's at lean of peak settings. Never had it runaway on me ROP.

[jlunseth]

I do have a couple of questions for the OP.  FIrst, when I watch the video, the fuel flow drifts up from around 10.0 to 10.9 at which point your CHT2 warning starts to flash and then the fuel flow climbs rapidly.  At that point, where the CHT starts to flash, did you turn the low boost on?  Boost pumps are not used in the 231 for any normal regime of flight.  They can be a help during starting if used right, and they are there in the event of an emergency caused by a malfunctioning mechanical pump, but otherwise they are not used.  If you are turning the low boost on at that point, that is what is causing the runaway fuel flow that rises rapidly about 1 GPH, which in turn drives the MP up.  

Second, have you checked the effect of opening the cowl flaps since you had the Merlyn removed?  The immediate effect of opening the cowl flaps is to change the air pressure inside the cowling, so a leak in the Merlyn would have been my guess also, but if it is still going on with the Merlyn removed, then it has to be something else.  

Do you have a fuel flow readout on your JPI that you could click through to?  It would be interesting to know if the fuel pressure is changing, or just the fuel flow.  

I would start by just adjusting the red knob down when the drift starts.  In my engine, sometimes it takes a couple of adjustments to convince the fuel flow to stablize at your desired number.  

[Bob]

1 hour ago, jlunseth said:

I do have a couple of questions for the OP.  FIrst, when I watch the video, the fuel flow drifts up from around 10.0 to 10.9 at which point your CHT2 warning starts to flash and then the fuel flow climbs rapidly.  At that point, where the CHT starts to flash, did you turn the low boost on?  Boost pumps are not used in the 231 for any normal regime of flight.  They can be a help during starting if used right, and they are there in the event of an emergency caused by a malfunctioning mechanical pump, but otherwise they are not used.  If you are turning the low boost on at that point, that is what is causing the runaway fuel flow that rises rapidly about 1 GPH, which in turn drives the MP up.  

Second, have you checked the effect of opening the cowl flaps since you had the Merlyn removed?  The immediate effect of opening the cowl flaps is to change the air pressure inside the cowling, so a leak in the Merlyn would have been my guess also, but if it is still going on with the Merlyn removed, then it has to be something else.  

Do you have a fuel flow readout on your JPI that you could click through to?  It would be interesting to know if the fuel pressure is changing, or just the fuel flow.  

I would start by just adjusting the red knob down when the drift starts.  In my engine, sometimes it takes a couple of adjustments to convince the fuel flow to stablize at your desired number.  

My 830 is set to flag me for high CHT at 390.  While attempting to diagnose the issue, I have done some things that I never do during normal operation, including letting CHT's go up to 400 and using the low boost pump.  The low boost pump was not used at all in the video.  I do understand that both boost pumps are their in the event that the mechanical pump fails. The low boost pump (about 10gph) is used if the mechanical pump fails in cruise, while the high boost pump (about 20-25 gph) is used if the mechanical pump fails during climb.

The Merlyn was removed a year ago, so is not the cause of this problem.

The JPI 830 has fuel flow, but not fuel pressure.

It will be interesting to see what happens when I reduce the mixture, when MP & fuel runaway.  Will a slight mixture reduction bring it down to where I was at 10gph or much lower like 8.5.  I'll update after I try it.  I feel a little stupid for not trying mixture, but have tried many things during the high work load on solo test flights while taking video and watching for traffic.  Oh, ya and almost forgot, I was also flying the plane. 

I am attempting to diagnose what is changing, when not touching anything.  Something is changing, Turbo speed, fuel flow or a leak may be sealing causing the MP to raise, etc

[jlunseth]

Got it.  Don’t feel dumb about not trying the mixture.  It is a little bit of an adjustment, if you have flown ROP most of your pilot career, to think of the red knob as the power control, but on the LOP side, it is.

That is a significant flow runup that you are experiencing though.  Adjusting the red knob will help you get on top of it, but given the size of the runup (about 2 GPH), and the speed of the runup, there seems to be some kind of error in your fuel control system.  Could be the linkage, or something else simple.  I am leaning towards your “spider,” the fuel distribution system on top of the engine.  Unfortunately, I am not a mechanic and don’t know the spider very well, so maybe someone else can help with what might be wrong.  

If you find yourself with that runup going out of control, you can just fly on the ROP side to get home.

[Cardinal767]

Here is a good read on the components in our engine fuel system. Their purpose and troubleshooting guide. 

http://www.dgsupply.com/node/2044

Edited April 5, 2018 by Cardinal767

[jlunseth]

That's a helpful document.  I caught this from it: "The metered fuel is delivered by the injector to a pressurized flow divider which distributes the fuel to the individual cylinders via dedicated lines and nozzles. The flow divider is a simple spring loaded valve that is sealed to atmosphere by a diaphragm. The valve movement and resulting fuel flow is strictly regulated by pressure acting on the valve. At idle, the fuel pressure must build to overcome the spring and diaphragm load in order to move and open the fuel ports. Metering at this speed is primarily a function of the flow divider but as flow increases and the valve opens, the fuel nozzles become the primary system metering components."  My emphasis.

This seems to say there is a pressure regulator (valve) in the system that appears to be affected by atmospheric pressure to a degree.  If this valve is not responding as it should (its sticking), and then it "unsticks" you would see exactly your symptoms, fuel flow would increase because the valve is opening as it should have earlier in the process.  Further, opening the cowl flaps might affect it because you are changing ambient pressure.  From the description, it looks as though the building fuel pressure fully opens the valve and from that point the injectors regulate fuel flow.  That suggests that, if it is opening late, you should find that dialing the fuel flow back with the red knob will stabilize the fuel flow.  If it does, then you have your culprit.  

As I said, I don't know the spider, so this is alot of guess on my part, just trying to be helpful.  There are other possibilities, the injectors could be clogging and then opening because of some kind of contamination or debris in the fuel, for example.

Good luck.

[FBCK]

I have an 1981 231 with the Myrlyn Waste-gate and turbo plus inter-cooler and experience the same thing.  May not to quit as fast as yours, but I find when  it starts to move its not a linear move up.  I can tell by the speed of the plane, a small move in fuel on the LOP side translates to a great difference in speed and hence HP.  I dial the mixture back and all is good.  Not a lot of work, but it is something I monitor in cruise.

[jlunseth]

35 minutes ago, FBCK said:

I have an 1981 231 with the Myrlyn Waste-gate and turbo plus inter-cooler and experience the same thing.  May not to quit as fast as yours, but I find when  it starts to move its not a linear move up.  I can tell by the speed of the plane, a small move in fuel on the LOP side translates to a great difference in speed and hence HP.  I dial the mixture back and all is good.  Not a lot of work, but it is something I monitor in cruise.

My experience is the same as yours.  His run-up in fuel flow, though, went from 9.8 to 11.7 at least.  It drifted up for awhile, got to 10.9, and then took off running, requiring intervention.  So there is something other than what you and I see going on.  I will get a little rise, maybe .5 gph or a little more, and it will be a slow rise.  I just dial it down, maybe have to repeat it once or twice, and then it stays.  It might drift around in a range of .3 or .4 GPH, but basically is stable.

[N231BN]

That's a helpful document.  I caught this from it: "The metered fuel is delivered by the injector to a pressurized flow divider which distributes the fuel to the individual cylinders via dedicated lines and nozzles. The flow divider is a simple spring loaded valve that is sealed to atmosphere by a diaphragm. The valve movement and resulting fuel flow is strictly regulated by pressure acting on the valve. At idle, the fuel pressure must build to overcome the spring and diaphragm load in order to move and open the fuel ports. Metering at this speed is primarily a function of the flow divider but as flow increases and the valve opens, the fuel nozzles become the primary system metering components."  My emphasis.
This seems to say there is a pressure regulator (valve) in the system that appears to be affected by atmospheric pressure to a degree.  If this valve is not responding as it should (its sticking), and then it "unsticks" you would see exactly your symptoms, fuel flow would increase because the valve is opening as it should have earlier in the process.  Further, opening the cowl flaps might affect it because you are changing ambient pressure.  From the description, it looks as though the building fuel pressure fully opens the valve and from that point the injectors regulate fuel flow.  That suggests that, if it is opening late, you should find that dialing the fuel flow back with the red knob will stabilize the fuel flow.  If it does, then you have your culprit.  
As I said, I don't know the spider, so this is alot of guess on my part, just trying to be helpful.  There are other possibilities, the injectors could be clogging and then opening because of some kind of contamination or debris in the fuel, for example.
Good luck.

The metering valve in the spider would have to be wide open already on takeoff or you wouldn't get anywhere near enough FF.

[jlunseth]

Yes, I thought of that, but the OP pulls the fuel flow back at least as low as 10 GPH, which is 40% of takeoff fuel flow.  My thought was that the valve might start to close at the lower fuel flow, and then open back up again, which would increase the fuel flow.  Maybe the valve doesn’t work that way, I don’t know, as I said, I am no expert on the spider.

[jackn]

I’m no expert on the LB engine, but it looks like a bootstrap situation. The MB & SB engines can’t do that because of the APC(when they’re working properly). It appears to me that the automatic wastegate is not working. 

[Bob]

Cardinal767- Thanks for the link!  http://www.dgsupply.com/node/2044

jlunseth- Some engines have a external fuel pressure regulator.  My engine does not.  I understand that the MP and FF will dance around a little, .2-.4in and .2-.3gph.  As you said, mine is way beyond that.  The 2gph and 3in problem happens about 10-12 times per hour.  The fuel manifold (spyder) is one possibility.

jackn- I do not have an automatic wastegate.  It is a ground adjustable, fixed bolt wastegate.  It does not change at all until a mechanic physically changes it.

I appreciate the help and suggestions that everyone has offered here!